Eddie Izzard?..

Have just finished watching this myself and came on to see what reception it got.

I can't be totally sure as I wasn't watching that intently as was distracted for parts of it but I don't think Eddie was a priest. The priest was a black guy singing with the rest of the choir and later on he takes confession from James Gandolfini's character, Nick. If you noticed there was also a nun singing mingled in amongst the choir too.

Even though Eddie's attire had the illusion of being accompanied by a [kind of] dog collar. He was actually dressed in some kind of burgundy pinstripe suit or blazer with a long cuff dress shirt benneath it and I think the collar of which is just peeping over the top mimicking a dog collar.

He's also shown later on nearer to the end of the film once again at the organ and he has a plain black jacket and an open collared white shirt with the top button undone and a third time in what appears to be a black polar neck jumper. The priest is up at the alter wearing white vestments singing along with choir boys by his side.